Variable resistance memories are now drawing attention as large-capacity memories that are to replace flash memories known as large-capacity semiconductor memory devices.
A variable resistance memory is a memory in which two-terminal variable resistance elements each having a variable resistance layer interposed between two electrodes are used as memory elements. In such a variable resistance memory, information writing and erasing are performed by utilizing reversible changes in a variable resistance layer between a high-resistance state and a low-resistance state due to the history of voltage application between the electrodes. Even if the voltage between the two electrodes is cut off, the resistance state of the variable resistance layer is maintained. Therefore, “variable resistance memory” is a type of nonvolatile memory.
Variable resistance elements are classified into several types based on the types of variable resistance layers and electrodes. Redox variable resistance elements that utilize movement of oxygen defects of transition metal oxides, ion-conducting variable resistance elements that utilize movement of metal ions or the like in the variable resistance layers, and the like are known.
Materials with relatively high compatibilities with the materials used in silicon CMOS processes are used in ion-conducting variable resistance elements. Therefore, those ion-conducting variable resistance elements are drawing attention as the next-generation semiconductor memory elements. For example, variable resistance elements in which a thin amorphous silicon film is formed as a variable resistance layer on a p-type highly-doped silicon substrate, and a silver electrode is formed on the variable resistance layer are known.
However, the above described ion-conducting variable resistance elements have the following problems the inventors have found. In each of the above ion-conducting variable resistance elements, one electrode (hereinafter also referred to as an ion source electrode) is made of silver, which supplies ions, and the other electrode (hereinafter also referred to as an opposite electrode) is made of highly-doped silicon.
In a case where such variable resistance elements are used as storage elements in a large-capacity storage device, a stack structure that is of a cross-point type and has storage-element-containing films stacked on one another needs to be formed to achieve a large capacity. In this case, the storage elements arranged in the same layer share an opposite electrode, and there is write current leakage or read current leakage between adjacent cells via the opposite electrode and the wirings connected to the opposite electrode.